I'm working on web site in which a "ribbon" submenu pops up as soon as the mouse touches one of the main menu items. I'm trying to explain to the designer that it should wait until the cursor has rested on the menu item, and not pop up when the mouse just happens to pass over it. I'm not sure how long (in milliseconds) that wait should be.

I can't link to the web site in question, but I figure the same principle applies to standard tool tips. How long should it take for a tool tip to pop up?

This is an appeal to authority with no evidence that those library authors are particularly good at UX, or how they decided on their defaults.
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IMSoPFeb 24 at 11:49

1

For what is worth, after revisiting my answer, I don't even think this is correct. Whatever approaches to delay=0 I think is better. But again, this is backed up only by my own experience and knowledge on the topic.
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IgnacioFeb 25 at 12:41

IF you fade the tool-tip in slowly you can start as soon as the mouse rests on the hot-spot. Just remember to cancel the animation when the mouse moves out that way if the mouse only slides over for a second the tool-tip wont show and if the user stops but then moves on you don't have a tool-tip showing on the wrong part of the page.